Photographic material



Aug. 1967 J. J. KINSELLA ET AL 3,333,981

PHOTOGRAPHI C MATER IAL Filed Jan. l7, 1963 INVENTORS JOHN J. KINSELLA FIG-2 B ROBERT A.WILFERTH M 75M W ATTORNEYS United States Patent 3,333,981 PHOTOGRAPHIC MATERIAL John J. Kinsella, Rochester, and Robert A. Wilferth, Pittsford, N.Y., assignors, by mesne assignments, to Technical Operations Incorporated, a corporation of Delaware Filed Jan. 17, 1963, Ser. No. 252,098 11 Claims. (Cl. 117-34) The present invention relates to silver halide photographic materials, and more particularly to such materials fabricated by means of evaporation of the silver halide under reduced pressure and elevated temperature conditions, and the condensation of the silver halide vapors upon a suitable substrate material. The silver halide vapor condenses as a stratum of silver halide microcrystals supported on the substrate by adherence of the microcrystals directly to the substrate and directly to each other. This material is to be distinguished from emulsion or gelatin silver halide photographic materials, in that in the latter the silver halide grains are supported in a binder matrix which isolates the grains from each other and from the substrate, and functions as the means for supporting the grains on the substrate. Accordingly, the evaporated silver halide stratum may be looked upon as binder free, and by this term it is meant to distinguish the present materials from the emulsion or gelatin type of silver halide photographic materials.

Silver halide photographic materials include silver bromide, chloride, and iodide, and mixtures thereof. For most photographic purposes, silver bromide is used as the dominant silver halide ingredient, with smaller amounts of the iodide and/or chloride included for particular effects or properties. Accordingly, although the specific examples employed for purposes of illustrating the present invention relate to silver bromide because it is the most important photographic silver halide, the invention is not to be construed as limited thereto.

Several attempts are reported in the prior art to provide evaporated silver halide photographic materials, as illustrated by the U.S. Patents 1,970,496 and 1,999,088 to De Boer et al., the U.S. Patent 2,945,771 to Mansfeld, and the French Patent 1,267,623 to Lu Valle, et al. The De Boer patents relate to a flash evaporation of silver bromide, wherein a charge of silver bromide is adhered to an open filament, and then is flash evaporated in a matter of a few seconds, under low pressure conditions, to a substrate. Mansfeld converted the De Boer flash evaporation process into a continuous process, by evaporating the silver halide from a crucible and onto a moving substrate web. Lu Valle added to the foregoing teachings further refinements in the manufacture of this type of photographic material. In our work in the art of manufacturing evaporated silver halide photographic materials, we have found that the foregoing prior art teachings are lacking in one or more aspects, with respect to the manufacture of an evaporated silver halide photographic material that can be economically competitive with emulsion materials. At the same time we have discovered certain improvements in the manufacture of this material that enhance the photographic qualities of the product.

In the De Boer procedure, it is stated that the silver bromide is applied to an open filament and is flash evaporated over a period of some seconds as the filament is heated to about 700 to 800 C. Since silver bromide melts at 434 C., it is apparent that during the few seconds of the evaporation operation, substantial evaporation begins at the melting point and continues in the ensuing seconds as the temperature of the silver bromide rises to some unknown value. Since the character and properties of the deposited silver bromide is dependent upon the temperature of evaporation, the resultant stratum will be nonuniform in its photographic properties. Furthermore, since the flash evaporation is basically an uncontrolled and indefinite procedure, it is apparent that successive coatings of successive photographic plates will vary in properties, and no uniformity of product would be obtained.

To some extent, at least, the De Boer problems are overcome by the teachings of Mansfeld and Lu Valle. However, both Mansfeld and Lu Valle expressly teach that when evaporating silver bromide under relatively continuous and stable conditions from a crucible, the silver bromide should not be heated above its decomposition temperature, which is reported in the literature as 700 C. In the brie-f heating period of De Boer, it is likewise quite unlikely that any material portion of the silver bromide could be heated to above 700 C.

Contrary to the prior art teachings, however, We have found that high vacuum evaporation of silver halide can be effectively conducted from a pool of the molten silver halide at temperatures substantially in excess of the decomposition temperature of the silver halide. For example, we have successfully evaporated silver bromide at temperatures in excess of its decomposition temperature and up to pool temperature of about 765 C., while condensing the vapors on conventional photographic substrates such as baryta paper, triacetate film and Cronar. The products exhibited photographic properties comparable to those produced under evaporation temperatures well below the decomposition temperature. Indeed, the higher temperature of evaporation has produced photographic strata with higher photographic speeds than strata produced under the same conditions except for the use of lower evaporation temperatures. The principal advantage of evaporating at higher temperatures, however, is the ability to coat the substrate at a much faster rate. For example, when evaporating silver bromide from a molten pool with a pool temperature of about 620 C., as compared with a' silver bromide pool temperature of about 765 C., for the same thickness of coating the latter temperature affords a rate of deposition about ten times faster than the former temperature. This unusual increase in deposition rate exists despite the defeating function of decomposition of the silver bromide at this elevated temperature. For example, if one were coating a substrate web by evaporating the silver bromide under high vacuum from a molten pool contained in a crucible equal in length to the width of the web and 25 inches wide, at an evaporation temperature of 620 C. for the silver bromide, the web could be moved over the crucible at a rate of only about 44.0 ft./min. to produce a silver bromide stratum on the web of about 0.4 micron 'in thickness. On the other hand, using a silver bromide temperature of about 765 C., under the same conditions, the web could be moved over the crucible at a rate of about 440 ft./min. to produce a silver bromide stratum on the web of about 0.4 micron in thickness.

It is accordingly one object of the present invention to provide for a photographic stratum of evaporated silver halide, wherein the evaporation of the halide is effected under conditions of reduced pressure and elevated temperature in excess of the decomposition temperature of the halide.

Another object of the present invention is to provide for a photographic stratum of evaporated silver halide, wherein the evaporation of the halide is effected from a pool of molten silver halide under conditions of reduced pressure, and wherein the temperature of the entire molten pool is in excess of the decomposition temperature of the halide.

And still another object of the present invention is to provide for such a photographic stratum wherein the principal silver halide constituent is silver bromide.

Other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following exemplary detailed embodiments of the invention, had in conjunction with the accompanying drawings, in which like numerals refer to like or corresponding parts and wherein:

FIG. 1 is a schematic elevation view of a vacuum coating apparatus utilized in practicing the present invention;

FIG. 2 is a cross-sectional view of the apparatus of FIG. 1 taken along line 22 of FIG. 1; and

FIG. 3 is a cross-sectional view of the apparatus of FIG. 1 taken along line 3-3 of FIG. 1, but with the parts in a different operational condition than in FIG. 1 for illustration purposes.

An exemplary apparatus for high vacuum, high temperature evaporation of silver halide is schematically illustrated in the drawings. The apparatus comprises a base 10, having a plate 11 mounted on its top surface A bell jar 12 is removably mounted on the plate 11, the surface of plate 11 and contacting surface of bell jar 12 being appropriately ground and machined to afford a high vacuum seal therebetween. Evacuation of the volume under the bell jar is effected by a pump 41 through line 40. Obviously a suitable pumping system is employed to afford a high vacuum with a minimum of contamination in the atmosphere under the bell jar 12.

A platform 13 is mounted centrally on plate 11 by means of brackets 14, for supporting the evaporation crucible 32. Preferably the crucible 32, from which the silver halide is evaporated, can function as its own electrical heating element, as is afforded by forming the crucible of tungsten, for example. In such instance the ends of the crucible are shaped for the attachment of leads 34, one to each end, by means of clips 33 and 39, or the like. With the leads 34 connected to a suitable electrical power source 35, the tungsten crucible 32 functions as its own resistance heater for melting and evaporating the silver halide placed therein.

A suitable distance above crucible 32 and platform 13 is a stand 16 supported by legs 17. Stand 16 is formed with a central aperture 18, which is the present instance is conveniently rectangular in shape. This aperture is covered on its upper side by a stationary backing plate 19, and on its lower side by a removable shutter 20. Shutter 20 may be pivoted by rotation of shaft 30 through handle 31, from a position underlying and covering the aperture 18 to a position completely exposing said aperture, as illustrated in FIG. 3.

Stand 16 further supports a web feed apparatus comprising a take-up roll 23 and a feed roll 24. Roll 23 is rotationally supported by a pair of brackets 21 mounted on stand 16, while roll 24 is similarly supported by a corresponding pair of brackets 22. These rolls are positioned on stand 16 so as to enable the feed of a web 29 from feed roll 24 under the lip 19a of backing plate 19, thence across the aperture 18, out of the aperture past lip 19b, and to take-up roll 23. In this manner a web 29 of desired material may be fed from roll 24 to roll 23 across the aperture 18. When shutter 20 is removed from the aperture, the web 29 is exposed to vapors issuing from crucible 32 during its traverse across the aperture. The web is otherwise essentially shielded from such vapors by stand 16.

A drive for web 29 is effected by a motor 36 acting on shaft 25 through bevel gears 37, 38. At the upper end of the shaft 25, another pair of bevel gears 27, 28 connect drive shaft 25 to stub shaft 26, in turn coupled or connected to take-up roll 23.

As is conventional, all elements extending from inside the vacuum chamber to outside thereof, such as shafts 25 and 30, leads 34, and vacuum line 40, pass through suitable seals in plate 11.

In accordance with the procedures of the present invention, the crucible 32 is charged with a desired quantity of silver halide, as for example silver bromide, iodide or chloride, or mixtures thereof. Or if desired, a plurality of crucibles 32 may be placed on platform 13 and independently electrically heated, one containing one halide and the other containing another halide, or both containing the same halide. For most photographic purposes, the ultimate deposited vapor should be predominantly silver bromide. A web of conventional photographic base material, such as photobase paper, or an acetate or Mylar film, is wound on roll 24, fed across the aperture 18, and connected to roll 23. Shutter 20 is positioned to close aperture 18. The bell jar is then sealed to the plate 11, and the vacuum pump started to evacuate the chamber defined by jar 12 and plate 11. For purposes of the present invention the operating pressure within the bell jar or vacuum chamber may be pumped down to between about 10- and 10- mm. Hg. Preferably, however, a pressure between the orders of about 10* and 1O mm. Hg is found best suited to our purposes, with about 5 10 mm. Hg being the most convenient value. As the pressure within the vacuum chamber approaches the desired value, current is applied to crucible 32 to melt the silver halide therein, and bring it up to the desired evaporation temperature. In accordance with the present invention, this evaporation temperature is chosen to be above the decomposition temperature of the halide, and preferably substantially in excess thereof. For example, in the case of silver bromide the temperature of the molten pool of silver halide in the crucible 32 should be in excess of 700 C., the decomposition temperature of silver bromide as reported in the literature. The range of about 725 to 765 C. or higher is preferred, with the higher end of this range being the more efficient. Obviously, if too high temperature is employed, the rate of decomposition of the silver halide becomes so great that the efficiency of the process will be reduced. When the pressure and temperature have reached the desired values and are substantially stable (i.e., constant to plus or minus a few degrees (3.), the shutter 20 is opened to permit the vapors of the silver halide issuing from crucible 32 to impinge upon the web 29 in aperture 18 and to condense and crystallize there in microcrystalline form. In

addition, motor 36 is energized to drive roll 23, and there-.

by advance web 29 across the aperture 18. The rate of feed of the web can be used to control the thickness of the silver halide deposit thereon for a given set of other operating parameters. Preferably, for maximum photographic properties, the silver halide deposit on web 29 should be very thin, in the range of a fraction of a micron, and preferably between about 0.1 and about 0.5 micron depending upon the specific substrate used, and the particular photographic properties desired.

In order to obtain a substantially uniform deposit of silver halide over the area of the web 29 as it advances across the aperture 18, it is preferred that the crucible 32 have a length at least approximating the width of web 29 or the corresponding width dimension of aperture 18. Also, it is apparent that web 29 must be located a sufiicient distance from the crucible 32 so as not to heat up'to a temperature that would inhibit the deposition of the evaporated silver halide thereon. For the silver bromide evaporating temperatures hereinabove suggested, it has been found that a distance from crucible 32 to the web in aperture 18 of about 3 inches is suitable. Under these conditions it was found that the web reaches a temperature of about 50 C. It is apparent that these physical parameters can be varied, and the web can be temperature controlled substantially independent of the spacing from crucible 32 by artificial or controlled cooling of the aperture-backing plate 19.

As previously stated, the prior art .admonishes against the preparation of evaporation silver halide layers for photographic purposes with evaporation temperatures in excess of the silver halide decomposition temperature. On the contrary, the findings of the present invention indicate that comparable photographic properties can be obtained with silver halide strata formed by evaporation at temperatures substantially in excess of the decomposition temperature of the silver halide, as compared with strata formed by evaporation at temperatures below the decomposition temperature; and indeed, higher photographic speeds have been obtained with the higher temperatures. In addition, with these elevated temperatures, the rate of coating or deposition of the silver halide layer can be increased many fold above that obtainable under prior teachings.

The following specific examples will further illustrate the present invention.

The samples of photographic material utilized in the examples tabulated hereinbelow are all prepared in the following manner. A Web of photographic quality baryta paper is inserted in the apparatus of the drawings in the manner above-described, the crucible is charged with pure silver bromide, for example silver bromide synthesized according to the procedures of Malinowski, described in The Journal of Photographic Science, vol. 8, 1960, pages 69-71, and the bell jar is sealed to the vacuum plate 11. In a period of about one hour the vacuum chamber is evacuated to a stabilized pressure of about 5 'l0 mm. Hg, and then the silver bromide charge is heated to a stable temperature of a value for each sample as indicated in the tabulation of examples. The shutter 20 is then opened and the paper web is advanced across the aperture 18 at a rate which effects a uniform deposit of silver bromide on the paper substrate of about 0.4 micron thick (which was found photographically optimum for this substrate material). Because of the residual gas load in the paper web, when coating is startedand the web advances, the pressure of the system rises to about 3X10 mm. Hg during the coating operation. The resultant photographic products, where similarly exposed to an optical image and developed, and the average relative photographic properties of these samples are set forth in the following table:

Approximate Evaporation Temperatures Average Average of Silver Speed Gamma Bromide Pool, C.

Example I 630 .05 0.8 Example II 715 09 0. 6 Example III 750 0. 5

Solution A Photographic grade gelatin: 1.25 g. diluted to 250 ml. with water.

Swell gelatin in 50 ml. cold water, make up to volume with boiling water, cool, and store in refrigerator.

Solution B Sodium carbonate: 78 g. anhydrous (or 91.26 g. of monohydrate) Potassium bromide: 2.0 g.

Water: q.s. to 1 liter.

Solution C Elon or Metol (N-rnethyl-p-aminophenol surface): 0.50 g.

' Sodium sulfite (anhydrous): 19.50 g.

HQ: 1.87 g.

Dissolve in water in the order: sulfite, Metol, HQ. Then dilute with water to 250 ml.

Make up developer of equal volumes of A, B, and C, and add ml. 1% sodium thiosulfate per /2 gal. of developer.

Having thus described the present invention and provided specific examples to facilitate a clear understanding thereof, it is apparent that various changes, modifications and variations will become apparent to those skilled in the art. Accordingly, it is not intended that the present invention be construed as limited to these examples, and such changes, modifications and variations as are embraced by the spirit and scope of the appended claims are contemplated as within the purview of this invention.

What is claimed is:

1. A method of vacuum coating silver halide composed at least predominantly of silver bromide onto a substrate comprising evacuating a housing having therein a crucible containing a supply of said silver halide and a web of substrate material spaced from said crucible to a pressure of between about 10 and about 10- mm. Hg, heating said silver halide and maintaining it at a substantially stable temperature between a temperature in excess of its decomposition temperature and about 765 C. while maintaining said pressure, and feeding said web past the mouth of said crucible to expose successive portions of said web to the evaporated silver halide to collect a photographically sensitive layer of the evaporated silver halide on said substrate material While said silver halide is maintained at said stable temperature, the rate of feed of said web being selected to deposit thereon a microcrystalline layer of said silver halide of less than about 0.5 micron in thickness.

2. A method of vacuum coating as set forth in claim 1, wherein said temperature is between about 700 and about 765 C.

3. A method of vacuum coating as set forth in claim 2, wherein said temperature is between about 725 and 765 C.

4. A method of vacuum coating silver halide composed at least predominantly of silver bromide onto a substrate comprising evacuating a housing having therein a crucible containing a supply of said silver halide and a supply of substrate material spaced from said crucible to a pressure of less than about 10- mm. Hg, heating said silver halide and maintaining it at a substantially stable temperature between a temperature in excess of its decomposition temperature and about 765 C. while maintaining said pressure, and exposing said substrate material to the evaporated silver halide to collect a photographically sensitive layer of evaporated silver halide thereon while said silver halide is maintained at said stable temperature, the exposure of said substrate material to said evaporated silver halide being no longer than that required to deposit thereon a microcrystalline layer of said silver halide of less than about 0.5 micron in thickness.

5. A method of vacuum coating as set forth in claim 4, wherein said temperature is between about 700 and 765 C.

6. A method of vacuum coating as set forth in claim 5, wherein said temperature is between about 725 and 765 C.

7. A method of vacuum coating as set forth in claim 4, wherein said substrate material is outgassing during the exposure thereof to the evaporated silver halide.

8. A method of vacuum coating silver halide composed at least predominantly of silver bromide onto a substrate comprising evacuating a housing having therein a container holding a supply of said silver halide and a supply of substrate material spaced from said container, heating said silver halide and maintaining it at a temperature between a temperature in excess of its decomposition temperature and about 765 C., and exposing said substrate material to the evaporated silver halide to collect a microcrystalline photographically sensitive layer of evaporated silver halide thereon while said silver halide is maintained at said temperature.

9. A method of vacuum coating as set forth in claim 8, wherein the exposure of the substrate material to the evaporated silver halide is not materially greater than I UNITED STATES PATENTS 1,970,496

8/1934 De Boer et a1 9694 2,945,771 7/1960 Mansfeld 117-106 3,219,488 11/ 1965 Lu Valle et a]. 11734 XR FOREIGN PATENTS 1,267,623 6/ 1961 France.

OTHER REFERENCES Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 3, p. 420.

WILLIAM D. MARTIN, Primary Examiner.

P. F. A'ITAGUILE, Assistant Examiner. 

1. A METHOD OF VACCUM COATING SILVER HALIDE COMPOSED AT LEAST PREDOMINATLY OF SILVER BROMIDE ONTO A SUBSTRATE COMPRISING EVACUATING A HOUSING HAVING THEREIN A CRUCIBLE CONTAINING A SUPPLY OF SAID SILVER HALIDE AND A WEB OF SUBSTRATE MATERIAL SPACED FROM SAID CRUCIBLE TO A PRESSURE OF BETWEEN ABOUT 10**6 MM. HG, HEATING SAID SILVER HALIDE AND MAINTAINING IT AT A SUBSTANTIALLY STABLE TEMPERATURE BETWEEN A TEMPERATURE IN EXCESS OF ITS DECOMPOSITION TEMPERATURE AND ABOUT 765*C. WHILE MAINTAINING SAID PRESSURE, AND FEEDING SAID WEB PAST THE MOUTH OF SAID CRUCIBLE TO EXPOSE SUCCESSIVE PORTIONS OF SAID WEB TO THE EVAPORATED SILVER HALIDE TO COLLECT A PHOTOGRAPHICALLY SENSITIVE LAYER OF THE EVAPORATED SILVER HALIDE ON SAID SUBSTRATE MATERIAL WHILE SAID SILVER HALIDE IS MAINTAINED AT SAID STABLE TEMPERATURE, THE RATE OF FEED OF SAID WEB BEING SELECTED TO DEPOSIT THEREON A MICROCRYSTALLINE LAYER OF SAID SILVER HALIDE OF LESS THAN ABOUT 0.5 MICRON IN THICKNESS. 